Add warning for type aliases that monomorphise a PolyKinds-ed type

Motivation

module B does not have -XPolyKinds and defines an alias type MySpecialP = MyPoly Bool

MySpecialP is monokinded, leading to confusing error messages down the line.

Proposal

Does it make sense to have a warning ("-Wmonomorphizing-alias"?) for this? For any type alias, check if the RHS involves PolyKinds, check that it does not have an explicitly mono-kinded kind-signature and that PolyKinds is disabled. If so, raise the warning.

For the unlikely case that the mono-kinded alias is desired, allowing an explicit kind signature to silence the warning seems appropriate.

I have no idea how complex this is to implement. If checking the above condition is too complex or is hard to do without false positives, feel free to close this.